What are we? Science was young when the ancient Greeks put forward a set of classical elements: from water, air, fire and earth; the Chinese believed in water, fire, earth, metal and wood. Still it was young and naiive. In this age of Large Hadron Collider in Geneva the Physicists would put down matter as made of twelve fundamental particles – quarks and leptons. These have no substructure and cannot be broken down into smaller particles. Quarks and leptons interact via four forces to make the universe we know today.
How these particles work to make matter.
The nucleus and the electrons are attracted to each other, exchanging photons. The force between the nucleus and electrons is the electromagnetic force.
Many atoms constitute objects in our everyday life as well as much bigger components of the universe such as stars and galaxies. The force dominating this level of macroscopic phenomena is gravity.
In an atomic nucleus a proton is made up of two up quarks and one down quark, and a neutron is composed of one up quark and two down quarks. The force that binds three quarks in a proton or a neutron is called the strong force and this force is due to exchanges of gluons. Having said this let us examine force mediator that facilitates exchanges. There are four such mediators the “gluon”, “photon”, “graviton” and “weak bosons”.
An atomic nucleus constitutes an atom together with electrons orbiting around it. The relation between the nucleus and electrons resembles the one between the sun and planets in the solar system.
In the centre of stars, huge energy is generated by nuclear fusion being mediated by weak bosons. This energy makes the universe bright. In nuclear fusion, a down quark is changed to an up quark by the weak force. Stars are luminous because the fundamental building blocks are changing their types and providing energy.
Quarks like to hang in groups
Although most physicists believe that quarks are the fundamental building blocks which make up the universe, no one has observed an isolated quark on its own. This is due to the nature of the strong force.
Like a nucleus and an electron that attract each other due to their electrical charges, quarks are combined together by their color charges.
Many atoms constitute objects in our everyday life as well as much bigger components of the universe such as stars and galaxies. The force dominating this level of macroscopic phenomena is gravity, intermediated by gravitons.
Experiments in 1968 provided the evidence for the quark model. The quark model actually explains the existence of more than 100 particles, all known as “hadrons” (as in Large Hadron Collider) and made up of different combinations of quarks. For example the proton is made of three quarks. If protons are hit hard enough, the strong force can be overcome and the proton smashed apart. With the LHC recently updated is powerful and the scientists are ready to look deeper into the world of quarks.
The Large Hadron Collider, famous for finding the Higgs boson, has now revealed another new and rather unusual particle. Pentaquarks are incredibly difficult to see; they are very rare and very unstable. This means that if it is possible to stick five quarks together, they won’t stay together for very long. The team on the LHCb experiment made their discovery by looking in detail at other exotic hadrons produced in the collisions and they way these break apart. All hadrons seem to be made up of combinations of either two or three quarks, whereas pentaquarks as the name suggests are made up of five quarks.
Why is this important?
The discovery answers a decades-old question in particle physics and highlights another part of the mission of the LHC. Discoveries of new fundamental particles such as the Higgs boson tell us something completely new about the universe. But discoveries like pentaquarks give us a more complete understanding of the rich possibilities that lie in the universe we already know.
By developing this understanding, we may get some hints about how the universe developed after the Big Bang and how we’ve ended up with protons and neutrons instead of pentaquarks making up everyday matter.(Ack: the Conversation,Feb15 of 2013,2015- Takashi Kobota/Gavin Hesketh)